Although most chefs and kitchen staff are used to working under pressure, there is a different type of pressure many are not aware of. Negative air pressure is a common hazard in commercial kitchens and can be the result of poorly designed or inadequate make-up air units, an essential part of a restaurant’s HVAC systems that is often overlooked.

A make-up air unit differs from a building’s standard HVAC systems in that its job is to make up for the air that flows out through exhaust fans, so that even when the ventilation system is operating at peak capacity, there is consistent airflow and the exhaust fan does not remove conditioned air from the premises.

“Restaurant owners and operators should consult with an HVAC expert if they are uncertain about their make-up air needs. Requirements vary from kitchen to kitchen, so make-up units must be customized for each application,” says Daniel Zacarelli, Manager, Technical Sales and Engineering for Enercare Commercial Services. “An inadequate supply of fresh air to compensate for the air being removed by exhaust fans can be dangerous and may violate building codes.”

Ensuring a proper supply of fresh air will enhance guest experience by keeping cooking odours out of dining areas and allowing for smooth entry door operation. Exhaust fans alone can create significant negative air pressure, making entry doors difficult for guests to open doors and causing them to close rapidly.

Maintaining efficiency and reducing risk

An inadequate supply of make-up air can cause a restaurant to dramatically increase its heating and cooling costs. Without adequate make-up air, restaurants are effectively sending energy dollars out the chimney in the form of higher bills, as well as indirectly placing a needless burden on other mechanical equipment, possibly reducing its useful life. On top of these costs, ventilation systems may also perform poorly, resulting in excess kitchen grease, air quality concerns and more seriously, increased risks of back drafting.

The problem is most serious in restaurants with open kitchens and establishments that use atmospheric water heaters, where the lack of an adequate make-up air unit can also prevent the escape of carbon monoxide.

The make-up air unit should supply 80 to 85 per cent of the incoming air, with the remainder coming from adjacent spaces. In addition, a slight negative air pressure (4.98 Pa) should be maintained for odour control.

Consult the experts

“We see inadequate make-up air units in large chains and independent establishments alike,” says Zacarelli. “The issue often arises when upgrades are made without consulting an HVAC expert and results in a decreased lifespan and increased operating costs for other equipment in the building.”

Each linear foot of venting in a commercial kitchen removes between 150 and 400 cubic feet of air per minute. When an equal volume of fresh air is not pumped back into the kitchen, the difference in air pressure can create an uncomfortably warm or cool environment for customers.

“Installing the right make-up air unit is affordable and convenient,” says Zacarelli. “With the right partner, it is easy to enhance the safety and comfort of staff and guests alike.”

Scott Beneteau is General Manager for Enercare Commercial Services, a leading provider of HVAC solutions for the restaurant and foodservice industry. Scott brings 15 years of experience as a trusted partner to organizations across a variety of sectors on issues including energy management and HVAC systems. Scott can be reached at For more information about Enercare Commercial Services, visit